Problem Statement
Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.
Note: For the purpose of this problem, we define empty string as valid palindrome.
Example
Input: "A man, a plan, a canal: Panama"
Output: true
Input: "race a car"
Output: falseSolution
Please note the special conditions:
- Ignore case
- Ignore any non-alphanumeric character
Lets run our simple two pointer system where:
- One pointer will start from left, while other start from extreme right end.
- Lets move left and right pointers untill they are pointing to a non-alphanumeric character
- Compare characters at both left and right position, check must be case-insensitive
Code
public static boolean isAlphanumeric(char c) {
return Character.isDigit(c) || Character.isLetter(c);
}
public boolean isPalindrome(String s) {
if (s.length() == 0) return true;
int l = 0;
int r = s.length()-1;
while (l < r) {
while (!isAlphanumeric(s.charAt(l)) && l < r) {
l++;
}
while (!isAlphanumeric(s.charAt(r)) && l < r) {
r--;
}
if (Character.toLowerCase(s.charAt(l)) != Character.toLowerCase(s.charAt(r))) {
return false;
}
l++;
r--;
}
return true;
}Complexity
Its O(n)
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